Pressure regulators such as those used in underwater breathing apparatus commonly employ the pressure differential between the ambient and a breathing chamber in the regulator to operate an air valve which supplies air to the breathing chamber. This is accomplished by mounting a flexible diaphragm across an opening in the wall of the breathing chamber and using the diaphragm to actuate the air valve. Since the breathing tube is connected to the breathing chamber, the diver breaths from the breathing chamber, and in single hose regulators the diver also exhales through the breathing chamber to the ambient.
When the diver commences to inhale while the air valve is closed, the pressure in the breathing chamber is reduced causing the diaphragm to be sucked into the breathing chamber and thereby to open the air inlet valve. When the user exhales, the pressure in the breathing chamber increases to cause the diaphragm to move out and thereby to close the air inlet valve. In order to reduce the effort required to breath from such regulators it is common practice to design the regulator so that a portion of the inlet air travels as a jet directly into the breathing tube, thereby to provide a so-called venturi effect which educts air from the breathing chamber and prevents the pressure in the breathing chamber from rising above ambient pressure. Consequently, the diaphragm is held in the pulled-in position by the venturi action and holds the air inlet valve open. While such a venturi effect makes it easier for the user to inhale from the regulator, exhaling becomes more difficult inasmuch as the venturi action must be overcome before the air inlet valve can be closed. Accordingly, the amount of venturi action provided must be carefully adjusted for optimum inhalation and exhalation.
In U.S. Pat. No. 4,140,113 there is described a demand regulator having a movable deflector for deflecting an increasingly greater portion of the inlet air away from the breathing tube as the air inlet valve is moved from the fully closed position to the fully opened position. The greatest portion of the inlet air is thus deflected away from the mouthpiece tube when the air inlet valve is fully open and the venturi action would otherwise be at a maximum. In actual practice the air inlet valve does not move to the fully open position during normal operation of a demand regulator. When, however, the air in the supply tank is nearly exhausted and the pressure of the air being supplied to the demand regulator is thus less than normal, i.e., the intermediate pressure is less than 140 p.s.i., the air inlet valve may move to the fully open position in an attempt to meet the inhalation demands of the diver. Under such circumstances the venturi action is relatively low because of the low air velocity wherefor it is unnecessary to deflect any of the inlet air away from the breathing tube to reduce the venturi effect.
In other types of demand regulators stationary deflectors are used to alter the direction of inlet air flow relative to the breathing tube and the breathing chamber within the regulator thereby to provide some venturi action for assisting the diver to inhale through the regulator. Since the venturi action is greatest when the air inlet valve is fully open and air flow is at a maximum, such regulators may have a tendency to free flow, and moreover, exhaling becomes more difficult inasmuch as the venturi action must be overcome before the air inlet valve will close.